The appearance and maintenance of traits like sexual reproduction will occur only if a net benefit exists to the fitness of individuals with those traits. Sexual reproduction comes with costs; for example, finding a mate can demand considerable time and energy. More importantly, individuals engaging in sexual reproduction only pass on half of their genes to each offspring, so their fitness is half that of asexually reproducing individuals. Scientists have examined the costs and benefits of sexual reproduction and determined that it is most likely to have evolved as a way to maintain genetic diversity. Experiments have shown that populations in erratic environments or those who are reproductively isolated from the rest of their species are at an advantage when they reproduce sexually rather than asexually. By being able to mix and match alleles, individuals within these populations can maintain genetic diversity and phenotypic variation, expanding their tool kit as a hedge against an unpredictable future.